1. Field of the Invention
This invention relates to a method and an apparatus for a thin film growth of silicon and the like on a semiconductor crystal substrate of silicon and the like.
2. Description of the Prior Art
In a reaction vessel 3 of a conventional thin film growth apparatus shown in FIG. 6 (FIG. 6 is a schematic cross-section of the apparatus.), in the case of growth of the thin film 9 on the semiconductor crystal substrate by introducing a raw material gas 5 of silicon or organic metal gas in a gas phase, a material consisting of the same constituent like the thin film 9 will be deposited on the inside wall surface 3a of the reaction vessel 3 which is kept at high temperature. A protruding surface defect and a stacking fault may be formed on the thin film 9 by adhering the material which is exfoliated from the wall and transferred on the substrate 1 during the film growth.
To prevent a deposition of the material on the inside wall surface a so-called "cold wall" type reaction vessel in which a temperature of the wall of the reaction vessel 3 is kept much lower than that of the substrate 1 has been employed, therefore, the temperature of the wall of the reaction vessel 3 is controlled at low temperature throughout thin film growth. An embodiment of effective cooling technology of the reaction vessel 3 is described in JP-A-57-2527, and JP-A-60-110116.
In FIG. 6, 2, 4, 6a and 11 denote as a susceptor, an infrared heater, a cooling gas for the inside wall 3a of the reaction vessel 3, and an exhaust, respectively.
As a preliminary procedure before thin film growth in gas phase, usually, there is an etching procedure so as to remove a natural oxide film on the surface of the substrate 1 by maintaining the temperature of the substrate 1 in a certain temperature in hydrogen atmosphere as a pre-heat treatment or by introducing HCl gas. In this case, impurities which are evaporated from the substrate 1 by an external diffusion or etching are to be adsorbed on the inside wall 3a of the reaction vessel 3, whenever the temperature of inside wall 3a of the reaction vessel 3 is kept at low temperature. The impurities adsorbed once on the inside wall 3a will be gradually dissolved, then transferred by gas flow to the growing surface of the substrate 1 and mixed with the thin film 9. As is explained above, during gas phase growth procedure, the impurities evaporated from the substrate 1 will be delivered gradually from the inside wall 3a and mixed with the thin film 9, that is a so-called autodoping phenomenon. According to this autodoping, there is a problem, in which an interface resistivity between the substrate 1 and thin film 9 will change widely, so a transient width TB becomes large, showing in the impurity distribution (refer to the profile B of a spreading resistance) in the conventional method given in FIG. 5.
When a plurality of thin film growth procedures are continuously conducted by a batch method, without introducing the etching procedure in which the material deposited on the inside wall 3a of the reaction vessel 3 is removed by flowing large quantity of HCl gas, the dopant will be kept in an adhered condition in the inside wall 3a, therefore, the resistivity of thin film thus formed on the substrate 1 will be decreased gradually batch after batch, even though a constant quantity of a dopant is supplied to the reaction vessel 3. Especially, just after a washed reaction vessel 3 is introduced, an influence of what is called a memory effect is very remarkable.
Furthermore, minority carrier life time is decreased once contaminants like a heavy metals are adsorbed on the inside wall 3a of the reaction vessel 3, and in the case of "cold wall" type, it takes long time for the recovery of the lifetime because the contaminants will be delivered gradually during the gas phase growth.